1. Field of the Invention
The present invention relates to the field of photography and, more specifically, to exposure control systems used in photographic apparatus and being configured for multiple ambient and flash illumination modes of operation.
2. Description of the Prior Art
The present invention relates to exposure control systems having one or more shutter and/or exposure aperture blades that are configured to be reversibly driven, stepwise, between terminal positions by an electrically controlled driver, such as an electrical stepper motor, for regulating the transmission of image forming light rays from a scene to be photographed along an optical path to a film unit located at the focal plane of a photographic apparatus such as a camera.
In general, such exposure control systems operate automatically or semiautomatically in both ambient and flash illumination modes of operation. For example, U.S. Pat. No. 3,950,766 and copending application Ser. No. 930,029 are directed to automatic exposure control systems wherein a stepper motor driven shutter is operated automatically in the ambient illumination mode under the control of a light integrating circuit that monitors the brightness of scene illumination and also operate automatically in the flash illumination mode wherein a follow focus system is utilized to select an optimum exposure aperture value in accordance with scene range distance as defined by the distance at which the objective lens is focused. U.S. Pat. No. 3,977,012 discloses a stepper motor driven shutter which operates in a semi-automatic mode wherein the operator manually sets exposure value in accordance with a photometer reading that is indicative of scene illumination brightness. These two patents and the copending application are assigned in common with the present application.
U.S. Pat. No. 4,065,776 is directed to an automatic exposure control system in which the stepper motor shutter is operated under the control of a scene light integrating circuit in the ambient light mode and utilizes a follow focus system for flash operation in which the lens focusing ring of the camera is coupled to a variable resistor so that the distance to the scene may be converted into a corresponding resistance value that is in the stepping motor control circuit for electrically regulating the shutter exposure aperture value in accordance with subject distance. In one embodiment the flash system operates in the follow focus mode wherein the exposure interval is fixed by an R-C circuit without regard for the effect of ambient light on scene illumination. In another embodiment the flash system operates in a hybrid mode wherein a photocell circuit monitors scene lighting and the exposure interval is determined by a combination of the follow focus set aperture value and the total scene brightness as defined by both the flash and ambient illumination.
While it is well known in the prior art to provide exposure control systems that feature stepper motor driven shutter and/or aperture mechanisms that operate in particular ambient and flash illumination modes of operation, including automatic, semiautomatic or manual setting modes, in general these systems do not provide the operator with the option to select among a plurality of ambient and flash illumination modes so that he may selectively override the automatic operation to exert some degree of creative or personal preference control over the photographic exposure or more closely optimize the exposure parameters for different types of flash illumination sources (i.e., incandescent flash bulbs vs. electronic strobe light).
Therefore it is a feature and object of the present invention to provide an exposure control system of the type wherein the shutter and/or aperture blade mechanism is driven stepwise by a driver such as a stepper motor and the system is programmable by the operator to operate in a plurality of ambient illumination modes and a plurality of flash illumination modes so that the operator may exert some personal preference control over the photographic exposure.
It is another object to provide such an exposure control system that is simple in construction and provides the operator with the choice of fully automatic or semiautomatic ambient illumination modes wherein the operator, under at least certain lighting conditions, may select the maximum exposure aperture to control depth of focus in the resultant photographic image when the system is operated in the semiautomatic ambient mode and also may select between a first flash mode wherein the shutter aperture blade mechanism is selectively programmed to operate in conjunction with an incandescent flash bulb source of relatively long duration and a second flash mode wherein the blade mechanism is preferentially programmed for operation with an electronic strobe flash source.
Another object is to provide such an exposure control system wherein the system may be set for selecting one of four possible modes of operation by the manipulation of only two switching devices that may be selectively set in any one of four possible combinations.
Yet another object of the present invention is to provide an exposure control system wherein digitally coded information, that sets the number of discrete steps that a shutter/aperture blade mechanism will be displaced by the stepper motor, from the closed position during an exposure interval, will be provided to the system's control logic circuitry in an unambiguous form, preferably in the form of binary coded numbers arranged in accordance with the Gray Code.
Other objects of the invention will in part be obvious and will in part appear hereinafter.